Method and apparatus for humidification of breathable gas with profiled delivery

ABSTRACT

A method and apparatus for delivering breathable gas to a user includes a humidifying unit that is controllable to humidify the gas in accordance with a variable humidity profile such that the gas is delivered to the user at variable humidity levels, e.g., during a treatment session.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/658,336, filed Jan. 24, 2007, which is the U.S. national phase ofinternational application PCT/AU2005/001156, filed Aug. 3, 2005, whichdesignated the U.S. and claims the benefit of U.S. ProvisionalApplication No. 60/599,864, filed Aug. 10, 2004, each of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Many humidifiers that are currently manufactured for patient respiratorydisorders such as Obstructive Sleep Apnea (OSA) are large, bulky, andhave large water reserves to treat most medical-related ailments such asdryness that may be caused by mouth leaks for example. Mouth leaks orany leaks for that matter release humidified gases to the atmosphere andbypasses the patient's airways where it is required. These heavyrequirements including those medical conditions requiring high levels ofcontinuous humidification may require humidifier devices with reservesas high as 600 mL of water. This increases the overall size and bulk ofthe Continuous Positive Airway Pressure (CPAP) Apparatus, ventilator,patient breathing air system, or gas supply system.

Where patients do not exhibit these inadvertent leaks or are onlyseeking lower levels of humidification, they are likely to be left withan unnecessarily oversized reservoir of remaining water at the end of atreatment session.

Furthermore, there are a substantial number of patients that onlyrequire relatively smaller amounts of humidification to marginallyimprove comfort to an acceptable level for a typical patient. Thesepatients for example may include those that only use their conventionalhumidifiers (ResMed HUMIDAIRE™ or Fisher & Paykel HC 100™) during thecooler months in winter for small but substantial gain in comfort byadding warmth and/or moisture to the airways that may dry due to theflow of air through the patient airways.

Current humidifiers are generally designed to fulfill the worst ailmentsand therefore require substantial humidification requirements. Thesesystems could be regarded as ‘overkill’ for a substantial population ofOSA patients who are only looking for a ‘comfortable’ level ofimprovement to undesirable dry and cool air.

Current and conventional humidification systems generally supply acontinuous level of humidification as set by the user and dependent onthe ambient temperature and humidity level. There are also systems thatmay modify humidification levels using a number of sensor arrays such astemperature sensors and/or humidity or flow sensors in aid to maximizeefficiency and/or synchronize with pressure or airflow. Theseconventional systems can maximize the performance of the humidifier bybeing able to deliver the maximum amount of humidity whilst reducing oreliminating condensation (e.g. cooler air can carry less moisture), alsoknown in the art as “rain-out”. However, these types of sensor systemsare complex and costly and still consume large amounts of water.

Accordingly, a need has developed in the art to address at least one ofthe shortcomings of the prior art humidifiers described above.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention to ameliorate the size and designconstraints of the conventional humidifier whilst delivering an adequateand comfortable level of humidification whilst consuming/delivering thefluid (e.g. water, core gas vapor, etc.) in an efficient manner(requiring lower liquid reservoir volumes) and delivered according tothe patient's needs, which may also be a manually selectable and/orprogrammable, semi-automated and/or automated delivery profile.

Another aspect of the invention relates to assisting patients lookingfor limited improvement to breathing comfort. However, the intention isnot to replace conventional, continuously heated humidifiers, but ratherto provide an additional choice more suitable for certain patients.

Another aspect of the invention provides profiled delivery of humidifiedgas to a patient.

Another aspect of the invention reduces water or fluid volume requiredby maximizing efficient use of water, which is a form of ‘rationing’.

Another aspect of the invention aims to improve breathing comfortaccording to patient selectable profiles in one embodiment.

These and other aspects will be described in or apparent from thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a blower according to an embodiment of thepresent invention;

FIGS. 2 and 3 illustrate sample humidity profiles for a patient'streatment session; and

FIG. 4 schematically illustrates an alternative embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a blower 10 according to an embodimentof the present invention. Blower 10 typically includes a housing 12 tosupport a blower motor 14 that pressurizes breathable gas for deliveryto a patient interface 16 (e.g., a mask) via an air delivery conduit 18that is connected to an outlet conduit 20 of blower 10. Blower 10includes a control panel 22 with one or more buttons and preferably adisplay. Blower 10 includes a pressure sensor 24 to provide a signal toa controller 26 (e.g., CPU) for control of blower motor 14, inaccordance with one or more control algorithms commercially availablefrom ResMed, Inc.

Blower 10 is optionally provided with a selectively attachable anddetachable humidifier unit 28 that includes a tub 30 and one or moreconduits 32, 34 that communicate with blower 10. Humidifier unit 28 mayinclude structure as detailed in U.S. Published Patent Application No.2004/0055597A1, incorporated by reference in its entirety. Humidifierunit 28 is in communication with controller 26, e.g., when conduits 32,34 are attached to blower 10.

In one embodiment, the operation and/or performance of the humidifierunit 28 is tailored or profiled to suit the patient's specifichumidification requirements. This in turn results in more efficientwater usage, and allows the capacity of the tub 30 to be reduced. Forexample, the capacity of the tub 30 can be less than 400 mL, e.g., from20 mL-400 mL or more preferably between 50 mL-200 mL. Of course, thevolume capacity can be greater or less, depending on application. Thisreduced volume allows the overall size of the blower humidifier and/orassembly to be reduced, thereby removing design constraints andfacilitating transport of the blower, e.g., during travel of thepatient.

Profiling may be intermittent or profiled in accordance to a patientselectable profile or according to a selectable or semi/automatedprofile typical of the treatment session's ambient environmentconditions.

Another embodiment may modify the delivery profile according totemperature of room over the course of a treatment session. The devicemay measure temperature versus time and predict what adjustments inprofile are desirable to maintain efficient fluid/water use.

In another embodiment the profile may change over a set time period oftreatment. For example, during an eight-hour treatment session, theprofile begins at start of treatment and continues on to either end ofsession or a set time period on the device.

The above can obviously be used in combination with other embodimentssuch as watching average room temperature or even monitoring temperaturechanges over a period of hours, days, weeks, or months, and can modifythe profile accordingly.

A profile may, for example, recognize that a typical bedroom tends tocool until the early hours of the morning where the temperature tends tostabilize before warming again by sunrise. Another profile that may beused may gradually reduce the humidity level during the course of thenight in one simple form of the invention.

In embodiments, the invention may also postpone delivery until a periodof the sleep session has passed. For example, a patient in the case ofCPAP does not tend to go to sleep (beginning of treatment session) withdry airways. Their airways are probably going to dry later, say one hourinto the night. Compared to conventional humidifiers used in OSA overeight-hour sessions, this feature alone can reduce humidification watervolumes by one-eighth.

When implementing the delay feature, valves 35 a and 35 b can be used todivert the path of the air so as to by-pass the humidifier unit 28 via aby-pass conduit 35 c. The air path is schematically illustrated in FIG.1 with a broken arrow 36. When shut, valves 35 a and 35 b form part ofthe respective walls of gas conduits within blower 10.

The invention in one preferred embodiment may cycle between switch onand off during the course of the night. These cycles can be regular,irregular, or otherwise controlled for numerous intervals and variousdurations using some smart electronic control. The switching off doesnot necessarily need to completely switch off, but may reduce intemperature during periods where less humidification is required. Asmentioned, this reduces water usage but may also lead to reduced energy(power) consumption and/or reduced running costs. For example,humidifier unit 28 may include a heater element to heat the volume ofwater. Heater element can be controlled via controller 26.

A user's manually selectable version is also possible. For example, asshown in FIGS. 2 and 3, a patient may set the humidifier device from amenu including, e.g., a Square wave or a Sinusoidal wave which may beintegrated into blower 10 or humidifier unit 28 in the form of a symbolon a dial or push button. The device then humidifies the air to a levelaccording to these changing profiles over a treatment session. In thecase of a Sinusoidal wave setting where the cycle starts as a ‘rise’,the humidifier level increases gradually to a maximum during the middleof a treatment session and gradually reduces to the end of the treatmentsession. The profile can be symmetrical or asymmetrical. Also, the delayfeature described above can be used in conjunction with the Squareand/or Sinusoidal wave, so that humidity is added only after treatmenthas commenced.

If the humidifier provides instantaneous humidification on demand, thisprofile may also be adapted on a patient breath-by-breath basis ratherthan over a full treatment session.

These profiles mentioned above can be any combination or variation of awave/curve and/or stepped. It may also be automated to learn the ambientenvironmental conditions. For example, a temperature sensor 40 (FIG. 1)may monitor room temperature changes over the annual seasons and modifythe profile further to gain maximum water/fluid use and efficiency. Forexample, during cooler months, the humidification profile may allow forlonger humidification periods (during the switch on or higher heatcycle) but not allow as high a level so as to reduce condensation andmaximize comfort for the patient.

Another embodiment may include a ‘fuzzy logic’ version where the user,with the assistance of the device's intelligence, provides an optimumhumidification profile, which provides optimal comfort to the patientwhilst maintaining efficient fluid/water usage. In this example, thepatient may wake up and press one of three buttons, or select a dialsetting, to indicate whether the level of humidification was “okay”,“too little” or “too much”. The device can then re-profile the deliveryaccording to the patient's perceived comfort level. In this case, muchof the actual profiling is automated.

Another embodiment of the invention considers two positive aspects ofhumidification and provides additional benefits. Current technologywarms the patient breathing air. Warm air is considered more comfortableto breathe especially if the ambient temperature is relatively low.Secondly, humidifiers add moisture to the breathing air. The inventionmay profile the humidity level at a different rate to that of the airtemperature. For example, according to the Sinusoidal wave settingexample mentioned earlier, the device may maintain warm breathing airwith minimal increased requirement at the middle of the treatmentsession. The humidity however may increase at an independent levelrelative to the temperature; for example, the humidity may increase muchmore than the temperature at the peak of the wave profile. This canagain be selected by a patient according to their comfort requirements.

Any of the embodiments mentioned above may have an ability to transferany ‘learned’ logic by memory storage media, or wireless communication(e.g. “Blue tooth” technology) so that the logic could be utilized by aphysician, another user, or else simply because the patient intends toreplace the device or upgrade to a newer model. Controller 26 mayinclude a memory 26 a to facilitate data storage/transfer.

In a more mechanized embodiment of the invention, a simple valve thatcontrols the humidified air entering the mainstream breathing air may becontrolled by mechanical links. For example, as shown in FIG. 4, arotating cam 42 that is profiled to control a valve 46 via mechanicallinkage 48, thus producing staged delivery of humidified gas through aconduit 49 (which may be conduit 34 in FIG. 1). The cam profile can besuch that the peak of the cam's lobe translates to largest valve openingand therefore greatest humidification level. The cam 42 could bedesigned to turn one revolution in one treatment session. The shape ofthe cam lobe determines the delivery profile. A bi-metallic spring mayalso be added to modify lift (generally reduce lift to reducehumidification as temperature decreases) and therefore forms a type ofmechanical temperature compensation.

Further to the above embodiment, the profile could be mechanicallyadjustable by a user. For example, a number of selectable pins aroundthe perimeter of a cam lobe could be push in or out to modify at whatperiod of the session and by how much to lift the valve.

In another embodiment, the invention may also incorporate a switch orsensor device that switches off the humidifier should the treatmentsession be interrupted. For example, an OSA patient may get up in themiddle of the night to go to the bathroom. This feature is designed toreduce water consumption further and also prevent condensation in theair delivery pipe, especially if the flow generator has stopped(ResMed's Smart Stop™ feature). It may also prevent the patientbreathing in condensate when they return to bed, which in turn improvespatient comfort.

Yet another embodiment of the invention includes a mask “rain-out”sensor 50 (FIG. 1) that does not require the use of humidity sensor likethe prior art. An infrared emitter and detector in communication withcontroller 26, e.g., are placed at the bottom of the mask interface orlocation where condensation is likely to bead or pool. The mask framewall in front of the side-by-side emitter/detector is transparent toinfrared light. Under normal conditions, the detector does not see anyinfrared light. If significant water droplets develop (condensation) infront of the emitter/detector, the light reflects back to the detectorand signifies condensation. The device may also use another type ofvisible or non-visible light emitter/detector combination.

The above feature applied to the invention may either reducehumidification or heating in response to “rain-out”, or otherwise it maymodify the humidification delivery profiles as described earlier toimprove patient comfort. Also by identifying “rain-out”, this mayprovide intelligence to the device's control that the ambienttemperature is falling or the heating of the delivered air is too low tocarry the current level of moisture.

One or more of the following advantages may be realized in accordancewith preferred embodiments of the invention:

-   -   Humidifier that is smaller, easier to store or travel with.    -   A device that can be tailored (profiled) or set by a user to        suit their circumstances, needs or desires for comfort.    -   A profile humidifier may bridge the gap between inefficient        “Passover” (non-heated) humidifiers and fully featured heated        humidifiers that treat most dry airway ailments.    -   Potentially less complaints of “rain-out” or condensation as        patients may have adjusted their device to a high setting, only        to find that a cooling room creates increased condensation.    -   Ability to control, modify and fine-tune their patient's        therapy.    -   By minimizing humidity delivery when it is not necessary reduces        water usage and reservoir volume required, therefore reducing        device size.    -   Alleviates the size constraints on engineers for the OSA market        that is trending towards fewer design compromises to meet        comfort expectations.    -   Flow generators have already been reduced in size, whereas the        humidifier is about the same size as next generation flow        generators, if not larger. This concept gives users the        perception of even more compact dimension that is potentially        lighter and easier to transport.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. For example, the above described preferredembodiments of the invention may be adapted to any humidification devicewhether to treat OSA or used in any gas breathing system.

1. A humidifier configured to couple to a blower adapted to provide asupply of pressurized breathable gas for providing continuous positiveairway pressure (CPAP) treatment to a patient, the humidifiercomprising: a tub adapted to hold a volume of water; a heater element toheat the volume of water; a temperature sensor to sense the ambienttemperature; a timer to monitor time and provide time for at least aportion of a treatment session; and a controller, wherein the controlleris configured to control the heater element to provide a humidityprofile during a treatment session, and the humidity profile isdetermined as a function of the sensed ambient temperature and the timeto maintain efficient use of the volume of water throughout thetreatment session.
 2. A humidifier according to claim 1, wherein thehumidity profile includes cycling the heater element on and off forpredetermined periods of time during the treatment session.
 3. Ahumidifier according to claim 1, wherein the humidity profile includesdelaying turning on the heater element for a predetermined period oftime at the beginning of the treatment session.
 4. A humidifieraccording to claim 3, wherein the predetermined time is one hour.
 5. Ahumidifier according to claim 1, wherein the humidity profile reducesthe humidity level during the treatment session and the initial humiditylevel is determined based on the ambient temperature and the timer.
 6. Ahumidifier according to claim 1, wherein the ambient temperature issensed over a plurality of treatment sessions to determine the humidityprofile.
 7. A humidifier according to claim 1, wherein the humidityprofile is determined from the sensed ambient temperature from one ormore previous treatment sessions.
 8. A humidifier according to claim 1,wherein the humidity profile is varied in response to the sensed ambienttemperature of the current treatment session and the timer.
 9. Ahumidifier according to claim 1, wherein the timer monitors and recordsthe time over the entire treatment session.
 10. A humidifier accordingto claim 1, wherein the timer counts down from a predetermined timevalue at the beginning of each treatment session.
 11. A humidifieraccording to claim 10, wherein the predetermined time value is theaverage length of time of a treatment session
 12. A humidifier accordingto claim 11, wherein the average length of time of a treatment sessionis determined from a plurality of previous treatment sessions.
 13. Ahumidifier according to claim 1, wherein the humidity profile isdetermined to prevent the tub from using equal to and/or more than thevolume of water during a treatment session.
 14. An apparatus forproviding continuous positive airway pressure (CPAP) treatment to apatient comprising: a blower adapted to provide a supply of pressurizedbreathable gas; a patient interface configured to deliver the supply ofpressurized breathable gas to the patient; an air delivery conduitbetween the blower and the patient interface; and a humidifier unit;wherein the humidifier unit includes a tub and at least one conduit incommunication with the blower, the humidifier unit being configured toprovide humidity to the pressurized breathable gas according to ahumidity profile, and the humidity profile comprises a setting thatcauses the humidity to vary during a treatment session.
 15. An apparatusaccording to claim 14, further comprising a control panel to allow thehumidity profile to be selected from a menu.
 16. An apparatus accordingto claim 15, wherein the menu includes at least one of a sinusoidal wavehumidity profile, a square wave humidity profile and a combinationthereof.
 17. An apparatus according to claim 14, wherein the humidityprofile is configured to vary the humidity in response to changes inambient environmental conditions.
 18. An apparatus according to claim17, wherein the ambient environmental conditions include at least one oftemperature and humidity.
 19. An apparatus according to claim 14,wherein the humidifier profile is configured to cycle between switchingthe humidifier unit on and off during the treatment session.
 20. Anapparatus according to claim 19, wherein the on and off cycles areconfigured to occur regularly throughout the treatment session.
 21. Anapparatus according to claim 19, wherein the on and off cycles areconfigured to occur irregularly throughout the treatment session.
 22. Anapparatus according to claim 19, wherein the off cycle is a period whenthe level of humidity provided is reduced compared to the level ofhumidity provided during the on cycle.
 23. An apparatus according toclaim 14, wherein the humidity profile is configured to delay the supplyof humidity for a predetermined period at the beginning of the treatmentsession.
 24. An apparatus according to claim 14, wherein the humidityprofile is configured to reduce the level of humidity provide over timethroughout the treatment session.
 25. An apparatus according to claim14, wherein the humidity profile is configured to provide humidity foronly a predetermined period of time of the treatment session.
 26. Anapparatus according to claim 14, wherein the humidifier unit comprisestwo conduits in communication with the blower, one conduit adapted tosupply the pressurised breathable gas to the humidifier and the otherconduit adapted to supply the humidified pressurized breathable gas backto the blower for delivery to the air delivery conduit.
 27. An apparatusaccording to claim 26, wherein the blower further includes a divertingmeans to divert the path of the pressurized breathable gas to a by-passmeans of the humidifier unit.
 28. An apparatus according to claim 27,wherein the diverting means includes a pair of valves to shut off thetwo conduits of the humidifier to prevent the pressurized breathable gasfrom entering the humidifier unit.
 29. An apparatus according to claim14, wherein the patient interface further comprises a sensor configuredto detect condensation.
 30. An apparatus according to claim 29, whereinthe sensor includes an infrared emitter and/or detector.
 31. Anapparatus according to claim 29, wherein the humidity profile isconfigured to adjust the temperature of the breathable gas in responseto a level of condensation sensed by the sensor.
 32. An apparatusaccording to claim 14, wherein the tub has a capacity in the range of 20ml to 400 ml.
 33. An apparatus according to claim 32, wherein the tubhas a capacity in the range of 50 ml to 200 ml.